Dutor

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
 
pthread_mutex_t mutex;
int global;
void * start(void * sid)
{
    for(int i = 0; i < 20; ++i)
    {
        //~ pthread_mutex_lock(&mutex);  // #1
        int j = global;
        //~ pthread_mutex_unlock(&mutex);// $1
        ++j;
        printf(".");
        fflush(stdout);
        sleep(1);
        //~ pthread_mutex_lock(&mutex); // #2
        global = j;
        //~ pthread_mutex_unlock(&mutex); // $2
    }
    return NULL;
}
int
main()
{
    pthread_t tid;
    pthread_mutex_init(&mutex, NULL);
    if(pthread_create(&tid, NULL, start, NULL))
    {
        printf("error creating thread.");
        abort();
    }
    for (int i = 0; i < 20; ++i)
    {
        //~ pthread_mutex_lock(&mutex); //#3
        ++global;
        //~ pthread_mutex_unlock(&mutex); // $3
        printf("o");
        fflush(stdout);
        sleep(1);
    }
    if(pthread_join(tid, NULL))
    {
        printf("error joining thread.");
        abort();
    }
    printf("%d\n", global);
    pthread_mutex_destroy(&mutex);
    return 0;
}